1. Field of the Invention
The technical field of the invention is that of powder compositions intended for the preparation of wet formulations for the construction industry, for example renders, mortars, concretes or adhesives for construction.
These wet formulations can be obtained:                directly by mixing the powder compositions on site (e.g. renders, mortars, concretes or adhesives for construction),        by mixing the powder compositions on industrial sites to produce prefabricated parts such as for example plates, concrete blocks or monomer blocks.        
More precisely, the invention relates to dry compositions based on mineral binders and a SuperAbsorbent Polymer (SAP) that are capable, after mixing with water at high mixing ratios, for example greater than 50%, of producing wet formulations that make it possible to produce lightweight hardened articles, such as exterior or interior coverings or renders (e.g. exterior thermal insulation system (ETI)/decoration/protection/waterproofing), adhesives, solid objects, etc.
2. Description of Related Art
In this technical field, there is a constant need for a “foam” system that incorporates air into the wet or hardened renders, mortars and concretes, so as to make them lighter and give them beneficial properties in particular as regards sound and/or thermal insulation and thermal resistance or fire resistance. These low-density wet render, mortar or concrete foams must also have good workability or handling. The sound and/or thermal insulation properties of these render, mortar or concrete foams would be particularly acceptable for floor coverings or resurfacing, exterior renders for protecting facades and firestop mortars, among others.
A certain number of admixtures for render, mortar or concrete compositions are already known, the function of which is to generate gases in situ and therefore to form a foam after mixing and porosity after hardening. This is the case in particular for aluminium powders capable of producing hydrogen in an aqueous or alkaline medium, as well as for hydrogen peroxide, which quickly releases oxygen when it comes into contact with catalysts such as silver or potassium permanganate. Other families of admixtures that generate gas in situ in a cementitious medium, such as oxygen, nitrogen, hydrogen, carbon dioxide, carbon monoxide, ammonia and methane, are described in U.S. Pat. No. 7,288,147B by the company Construction Research & Technology.
The lightweight blocks of the YTONG® type and the lightweight walls marketed by the company XELLA® are obtained by autoclaving blocks of calcium silicate that have previously been made lighter by introducing aluminium powder, which generates hydrogen. These prefabricated elements have properties of thermal insulation and mechanical strength allowing their use as structural elements (in the case of Thermopierre blocks, which have a lambda value close to 0.12 W/m·Kt and mechanical strength of 3-5 MPa approximately) or as non-bearing cladding elements, contributing additional thermal insulation (in the case of Multipor® cladding, which has a lambda value close to 0.048 W/m·K and mechanical strength of 0.5 MPa). Obtaining these elements requires aluminium powder to be handled, which requires particular precautions in view of its explosive nature. Moreover, a costly autoclaving stage is necessary to confer the necessary mechanical strength on these elements. This technique therefore cannot be used on site. Moreover, with respect to the production of prefabricated parts, there is a demand for alternative technologies for the production of prefabricated elements having the same types of mechanical and thermal insulation performance, which avoid the use of aluminium powder (eliminating the potential problems of explosion) and which avoid the costly autoclaving stage: energy cost, low productivity and specific investments.
Air-entraining admixtures are also known for renders, mortars and concrete, the purpose of which is to trap the surrounding air, during blending with water (mixing) of the dry compositions of renders, mortars or concrete. These air-entraining agents are for example surfactants, fatty acids and alkali salts of fatty acids such as sodium lauryl sulphate. Such known air-entraining admixtures are capable of improvement.
In fact, all of the difficulty of this route of production of foams by air-entrainment lies in the stabilization of the air trapped within the wet matrix of render, mortar or concrete.
This stabilization is even more problematical in that it must not be obtained to the detriment of the standard properties (e.g. ease of use) of the wet forms of render, mortar or concrete foams, or to the detriment of the properties (in particular mechanical) expected for the hardened forms of these foams.
Moreover, the stability of the foam must also be present at each stage of the preparation and application processes. This must be embodied by a density that does not vary during each stage, whether in the mixing vat, after passing through the pipes (lance output density l.o.d.) or during spraying, when the application is carried out in this way. Conversely, this density can be different between each stage. The reproducibility and reliability of the method of producing these foams, although problematical in an industrial environment, pose a real problem of robustness when use directly on site by unqualified operators is envisaged. In practice, their use on site is very limited as it requires highly qualified labour.
In order to improve this route of production of air-entraining foams, FR2955103A proposes a dry composition for the preparation of render, mortar or concrete foams for the construction industry, which become porous once hardened, so that they are lightweight, thermally and/or sound insulating, both in paste form and hardened form, and which are obtained by air-entrainment during mixing. This composition includes a foaming admixture comprising:                A. a modified starch ether having a Brookfield viscosity comprised between 500 and 25,000 mPa·s.;        B. a stabilizer comprising at least one linear polyacrylamide;        C. a film-forming polymer.        
FR2955104A relates to a thermally-insulating material with a cellular structure comprising by weight relative to the total weight of the material: −4 to 96% of a hydraulic binder characterized, before coming into contact with water, in that it comprises at least one phase chosen from C3A, CA, C12A7, C11A7CaF2, C4A3$ (ye'elimite), C2A(1-x)Fx (with C→CaO; A→Al2O3; F→Fe2O3 and x belonging to ]0, 1]), amorphous hydraulic phases having a molar ratio C/A comprised between 0.3 and 15 and such that the cumulative Al2O3 content of these phases is comprised between 3 and 70% by weight of the total hydraulic binder, −4 to 96% of at least one filler; said material having a coefficient of thermal conductivity at 20° C. that is equal to or less than 0.20 W/m·° C. This thermally-insulating material is obtained from a foam.
These aqueous foams according to FR2955103 & FR2955104 can be improved, as, on the one hand, their stability is not infallible, and, on the other hand, their blending with a cement slurry is an incorporation operation that must be carried out carefully in order to avoid breaking down these foams. Such an operation is difficult to carry out under on-site conditions and requires the use of specific machines.
It is also important that the gain in terms of being lightweight is not achieved to the detriment of the other properties required for structures obtained from the wet formulations of renders, mortars and concretes, produced from dry cementitious compositions. This relates to the properties of the wet formulation: ease of use, workability, “pumpability”, rheology, ease of blending and application, as well as cleaning the tools, and the properties of the hardened products obtained from this wet formulation: protection/waterproofing, thermal and sound insulation, hardness, crack resistance, flexural strength, compressive strength, and durability.
Patent application US2003/144386A describes mixtures of hydraulically setting building materials, comprising less than 2% by weight of particles of a size greater than 200 μm of a polymer capable of forming a hydrogel. In particular, US 2003/144386 discloses standard mortars prepared according to standard EN 196 (1,350 g of standardized sand-450 g of cement-225 g of water for mixing), in which are incorporated 0.5% by weight of the SuperAbsorbent Polymers (SAP) Hysorb® C3746-1 & C Hysorb® 3746-5 from BASF® having less than 2% by weight of particles of a size greater than 200 μm as well as a comparative SAP Hysorb® C 7015 from BASF® having substantially more than 2% by weight of particles of a size greater than 200 μm. These three mortars are compared with each other and with the standard mortar without SAP. The SAPs Hysorb® C3746-1 & C Hysorb® 3746-5 make it possible to increase the compressive and flexural strength of the hardened finished products obtained from these mortars, compared with those obtained via the standard mortar without SAP.
Patent application US2010/190888A describes a dry mixture of hydraulically setting building materials, preferably a tile adhesive in accordance with standard EN 12004, characterized in that it comprises:
a) 10 to 95 percent by weight of a cement-containing hydraulic binder,
b) 5 to 75 percent by weight of mineral fillers and/or organic fillers,
c) 0.5 to 10 percent by weight of a redispersible polymer powder,
d) 0.1 to 1.5 percent by weight of a water-retaining agent that is based on polysaccharide structures and is preferably chosen from the group constituted by ethers of methyl hydroxypropyl cellulose (MHPC) and/or methyl hydroxyethyl cellulose (MHEC),
e) 0.3 to 4.0 percent by weight of an additional setting accelerator chosen from the group constituted by calcium formate, calcium chloride, calcium nitrate and
fa) or fb) 0.02 to 2.0 percent by weight of an acrylic copolymer of the pulverulent anionic or cationic type, which is preferably capable of swelling by means of water or salt solutions and is particularly preferably insoluble in water and can advantageously be prepared by radical polymerization of unsaturated ethylene vinyl compounds; fa) or fb) having a particle size distribution that is determined in accordance with standard 420 EDANA.2-02, such that more than 98% by weight pass through a sieve having a mesh size of 200 μm. The compositions disclosed are:
Composite thermal insulationTile adhesiveTile adhesivesystema) CEM II A 42.5 Ra) Portland cement CEM Ia) Portland cement (for exampleCEM I 42.5 R)b) Lightweight silica fillerb) Silica sand and calcareousb) Silica sand or comminutedaggregateslimestonec) Vinyl acetate ethylenec) Vinyl acetate ethylenec) Vinyl acetate ethylenecopolymercopolymercopolymerd) Hydroxypropyld) Hydroxypropyld) Hydroxypropyl methylcellulosemethylcellulosemethylcellulose and starch ethere) Calcium formatee) Calcium formate acceleratore) Calcium formatefa) Copolymer 1 (anionic):fa) Copolymer 1 (anionic) orfa) Copolymer 1 (anionic) or0.96%fb) copolymer 2 (cationic): 0.30fb) copolymer 2 (cationic): 0.30 oror 0.45%0.4%Cellulose fibresCellulose fibresSodium bentoniteFeSO4—7H2OMixing ratio: 76%Mixing ratio: 36%Mixing ratio: 25%
The compositions according to application US2010/190888 aim to improve the yield, namely the ratio between the volume of the wet formulation and the mass of the dry mortar, for economic reasons (e.g. reducing the stocks of dry mortar). The use of calcium formate or other calcium salts contributes to the increase in the setting rate according to application US2010/0190888A.